Add answer to ex1.15 and fixed some format

Author: icgw

ch01/README.md

@@ -132,7 +132,7 @@ std::cout << /* "*/" /* "/*" */;
 
 Output:
 
-    /**/ */ /*
+    /**/ */ /* 
 
 ## [Exercise 1.9](ex1_9.cpp)
 ## [Exercise 1.10](ex1_10.cpp)
@@ -144,7 +144,7 @@ of sum?
 ```cpp
 int sum = 0;
 for (int i = -100; i <= 100; ++i)
-sum += i;
+    sum += i;
 ```
 
 the loop sums the numbers from -100 to 100. the final value of sum is zero.
@@ -213,7 +213,32 @@ using a while. Are there advantages or disadvantages to using either form?
 the box on page 16. Familiarize yourself with the messages the compiler
 generates.
 
-Nothing to present here.
+**Syntax Errors**:
+```c++
+int main(){
+    std::cout << "Hello World!" << std::endl // semicolon missed 
+    return 0;
+}
+```
+
+**Type errors**:
+```c++
+int main(){
+    char s = "Hello World!"; // Here char should be std::string
+    std::cout << s << endl;
+    return 0;
+}
+```
+
+**Declaration errors**:
+```c++
+int main(){
+    int k = 0;
+    std::cout << K << std::endl; // use of undeclared identifier 'K'
+    return 0;
+}
+```
+
 
 ## Exercise 1.16
 

ch01/ex1_9.cpp

@@ -2,19 +2,15 @@
 
 #include <iostream>
 
-using std::cin;
-using std::cout;
-using std::endl;
-
 auto sum(int lo, int hi)
 {
     int sum = 0;
-    while (lo < hi) sum += lo++;
+    while (lo <= hi) sum += lo++;
     return sum;
 }
 
 int main()
 {
-    cout << "sum is: " << sum(50, 100+1) <<endl;
+    std::cout << "Sum of 50 to 100 inclusive is: " << sum(50, 100) << std::endl;
     return 0;
 }

ch13/ex13_22.h

@@ -6,7 +6,7 @@
 //
 //  Assume that we want HasPtr to behave like a value. 
 //  That is, each object should have its own copy of the string to which the objects point. 
-//  We¡¯ll show the definitions of the copy-control members in the next section. 
+//  We'll show the definitions of the copy-control members in the next section. 
 //  However, you already know everything you need to know to implement these members. 
 //  Write the HasPtr copy constructor and copyassignment operator before reading on. 
 //